Pages

Monday, January 12, 2015

Selecting a Pump Housing and Coupling

Guest Post: Bob Buesing, Lovejoy Application EngineerAnyone who has ever tried to integrate an electric motor with a hydraulic pump, knows that it can be a challenge to solve the puzzle of matching a housing length to the coupling size with the least aggravation. Motors should be selected to meet application needs, however many are often selected based on availability rather than system requirements.

As with motors, pumps are often selected based on availability with the primary concern being that the pump can handle the oil flow requirements of the application. Hydraulic pumps are available in an assortment of pump face sizes, and each size has a variety of shaft sizes and lengths. With the assortment of domestic and international pump manufacturers in the market today, it is common to encounter a variety of standards governing the pilot size on the end of the pump, the bolt pattern used to anchor the pump to the housing, and the shaft options. Deep breath.

The selection issue then becomes how to take the variables related to the motor and motor shaft, and marry those to the variables associated to the pump and pump shaft. The greater the difference in the shaft parameters between the motor and pump, the more difficult it will be to find a housing and coupling that will allow you to integrate the two pieces of equipment. For example, there are combinations of shaft diameters that vary so greatly, they simply cannot be joined inside the same housing. The author senses a few smiles out there from those who have experienced this challenge.

Things To Remember

The first thing to remember when selecting a coupling to go inside a housing is that the coupling must accommodate what is called a “blind installation”. This means the hubs must slide together inside the housing, or literally inside a tube, with minimal human intervention to assist with positioning the hubs.

One hub must be mounted on the motor shaft, the second on the pump shaft, then the housing gets bolted to the face of the motor (or pump). The coupling might have size limitations, typically due to the need to fit through the pilot opening in the pump end of the housing. After the elastomeric insert or spider is placed in the jaws on one side of the coupling, the remaining piece of equipment gets positioned in the housing. Usually there is an access window in the side of the housing to allow for aligning the hubs so that the jaws and spider can mesh. This access window also allows the installer to check the gap between the two hubs to ensure the spider fits correctly.

This is when accurate measuring and careful math calculations become critical. The lengths of the motor and pump shafts, the length of the housing, the overall length of the coupling, the outside diameter of the coupling, and the spider gap requirements all need to be coordinated to ensure the spacing inside the housing works with the coupling selected. If the housing is too short, the shafts could butt up against each other. If they are too far apart, the coupling may not be able to span the gap. It is rare that the gap between shafts ends will match the spider width (or coupling gap) exactly and the hubs often need to be either pushed back on the shafts a small amount, or hang off the shafts a small amount.

In either case, it is always advisable to look at different housing lengths that are available to minimize issues associated with the amount of shaft separation. The hydraulics industry has published standards governing most housing sizes. Normally, the pump/motor mount housings have fixed lengths to meet these standards and custom housing lengths could have an impact on the cost.

Need Help with Selection? We Can Help!

For this reason, Lovejoy Application Engineering put together a tool for their own internal use to assist with determining the proper combination of a stock housing with a coupling to best satisfy these variables. It removes much of the guesswork from the housing and coupling selection while lowering the risk of purchasing the wrong combination.

The engineer simply enters the desired housing to be used, the NEMA frame size for the motor, the pump face and shaft information, the motor horsepower and speed, and the coupling choice. The selection tool provides feedback that confirms the selected combination will fit in the required space and accommodate the torque requirements, thus adding confidence to the selection process.

A Couple More Quick Notes

If the hub needs to be pushed back on the shaft, make sure the keyway is long enough that the key being used can be the same length as the hub. The opening in the spider or elastomeric insert must be large enough for the larger of the shafts to fit inside the spider. If this is a spline, you may be limited to how far the hub can slide back onto the shaft. If the coupling needs to hang off the shaft, it is a good practice to ensure the amount of engagement between the hub and the shaft is as close as possible to the diameter of the shaft. With splines, users must keep in mind that as much spline as possible must be engaged or lose some of the benefits of using a spline, possibly even jeopardize the strength of the spline. If a spline clamping feature is being used, this may limit the actual positioning of the hub on the spline shaft.

So, when you are looking to design a new hydraulic system, repair a current system, or even piece together a system using equipment that perhaps was not originally designed to be used together, feel comfortable contacting your local Lovejoy products reseller with all the details about your system. They can then work together with Lovejoy technical support to select your housing and coupling.

For the Quickest Response

Please do not send in the pump and motor manuals since these tend to be rather lengthy and do not always specify the exact details regarding your actual equipment. Please provide the following:1. Motor Horsepower and running speed.2. NEMA frame size. This gives us the motor shaft diameter, length, keyway size, and pilot information.3. Pump shaft size details to include diameter, length, keyway or spline details, and pilot details to include the diameter and width.

Further questions or feedback on pump housing and coupling selection can be directed to Lovejoy's application engineering team by email or by phone (630-852-0500).

About the Author:
Bob Buesing has a rich legacy of serving Lovejoy and Lovejoy's clients
as a coupling application engineer and product trainer. To tap into Bob
and Lovejoy's
rich
industry knowledge and experience, please contact call (630-852-0500)
or email Lovejoy and request to speak with an application engineer.